The present disclosure relates to toner additives. In particular the present disclosure relates to the incorporation of charge control agents in toner particles.
There is a continuing interest in developing technologies that reduce toner environmental sensitivity while increasing or allowing tailoring of toner charging properties for diverse applications. A particularly useful application uses bio-based resin toners for making toners from renewable environmentally friendly sources, or conventional or Emulsion Aggregation (EA) toner formulations for low melt toner which employ crystalline polyester (CPE) resins in the toner.
Improving the characteristics and performance of toner compositions is a continuing goal in the art. One area of improvement focuses on the resins used in making the toner compositions, as the resin comprises a substantial portion of the toner composition. In particular, one characteristic that has gained interest is the sustainability of the resin. As environmental concerns have grown, it has become important for manufacturers to reduce their carbon footprint and dependency on fossil fuels. One way to achieve this goal in connection with toner production is to use bio-based raw material feedstock to make the toners. However, such bio-based materials sometimes do not perform as well as their olefin based counterparts, primarily due to moisture sensitivity (moisture affinity) of bio-based resins leading to low toner charge in high humidity conditions of A zone. Temperature and relative humidity (RH) for the A-zone is typically about 80° F. and about 80% RH while for the B-Zone temperatures are typically about 70° F. and about 50% RH. Furthermore, the charge gap increases with increasing bio-based material content and limits the amount of bio-based resin that can be incorporated in the toner to be marketed as “green”. This diminishing return relationship is shown in Table 1.
TABLE 1Percent of BioBased ResinToner Charge (microcolumbs/gram)in TonerA zoneB zoneJ zoneFormulation(80 F./80% R.H)(70 F./50% R.H)(70 F./10% R.H)01824251513.520262012.521.526.52510.517233010.519234951421
Low toner charge leads to toner contamination in the machine (unwanted toner spits and toner puffs), which leads to dirty prints and unacceptable image quality. Thus, there remains a need to produce a bio-based toner composition that can perform on par with olefin based toner compositions.
The moisture sensitivity is also a problem when using crystalline polyester (CPE) resins, even when no bio-based resins are incorporated in the toner formulation. A particularly useful application of crystalline polyester (CPE) resins is in design for low melt toner (lower minimum fixing fusing temperature). The addition of as little as 15 weight % of CPE can lower the minimum fusing temperature (MFT) by as much as about 30° C. A lower MFT enables more energy efficient and faster printing speed machines. CPE can be added to both conventional toners and Emulsion Aggregation (EA) toners to lower the minimum fixing fusing temperature of the machine. Similar to bio-based resins, one issue with incorporating CPE in toner design is that the A-zone parent toner charging become drastically reduced with the incorporation of CPE resin into the toner. The more electrically conductive crystalline resin on the surface of the toner is believed to be responsible for the poor charging performance. This issue can be corrected by increasing the additive coverage, to compensate to balance the difference in charge. However, the increased additive coverage increases the cost, and can lead to other problems, such as aging in longer term tests. There is a need to increase the A-zone parent charge of toners comprising CPE, while at the same time having a beneficial effect of relative humidity (RH) sensitivity.
Charge control agents (CCAs) are organometallic compounds that have been added to toner formulations to increase the charge of toners. For conventional toners CCAs are often added to the toner resin and pigment mix during melt extrusion. In this case, the CCA is dispersed throughout the toner resin, rather than on just the surface where it can have maximum effect. Also it is difficult to control how much CCA is present on the surface of a conventional toner by this method. For EA toners, CCAs have been added during the emulsion/aggregation process or have been incorporated into the latex itself. However, it is difficult to control how much of the CCA is present on the toner surface. Moreover, incorporating CCA into EA toners involves several other challenges such as pH & temperature sensitivity of the CCA leading to their premature precipitation, high amounts of coarse observed during the process or inactivity-unpredictability of charge increasing behavior of the CCA.